The long-term goal of this research proposal is to provide insights into the molecular basis for antibiotic biosynthesis in bacteria, which will serve as a framework for the design of novel antibiotics. Recent work in biosynthetic combinatorial chemistry technology has already established the utility of bacterial polyketide synthases and nonribosomal peptide synthases in generating natural and un-natural products with antibiotic capabilities. We seek to extend the research of biosynthetic production of therapeutics by providing a framework for the use of lantibiotics, a family of ribosomally synthesized but post-translationally modified peptides. The engineering of these lantibiotics is complicated by the fact that any modification that are generated in the peptide precursor may affect its function as a substrate for the post-translational modification enzymes, and compromise the effectiveness of this approach. In order to delineate the substrate requirements for the post-translation modification enzyme, we aim to determine the high-resolution crystal structures of many of the lantibiotic modification enzymes. The crystal structures of these enzymes will be used to identify and design site-specific variants. We will test our structure-based hypothesis by correlating the structure with functional data generated in the laboratory of our collaborator. Additionally, we will determine the crystal structure of the immunity component that protects the lantibiotic-producing bacteria from the action of its self-produced drug. We seek to understand why lantibiotics that are nearly identical in sequence utilize immunity components that share no homology and vary drastically in size. Finally, we will utilize the mechanistic and structural data generated in the previous components of the research plan to engineer the production of novel lantibiotics. In this last aim, we will seek to utilize the principles of biosynthetic combinatorial chemistry to answer the question "Can novel lanthionine-bearing lantibiotics be designed from structure-based principles?"